Synthetic aircraft turbine oil

ABSTRACT

Synthetic lubricating oil composition comprising a major portion of an aliphatic ester base oil having lubricating properties formed by the reaction of a pentaerythritol or trimethylolpropane and an organic monocarboxylic acid containing from about 0.01 to 2.5 weight percent of an imminium salt of thiocyanic acid represented by the formula:

United States Patent [191 Nebzydoski et al.

[451 Oct. 23, 1973 SYNTHETIC AIRCRAFT TURBINE OIL [75] Inventors: John W. Nebzydoski; Edwin L.

Patmore, both of Fishkill; Frederick G. Oberender, Wappingers Falls, all of N.Y.

[73] Assignee: Texaco, Inc., New York, NY.

[22] Filed: Oct. 18, 1971 21] Appl. No.:'190,3i0

[52] US. Cl. 252/475, 260/566 R Primary Examiner-Patrick P. Garvin Assistant Examiner-Andrew H. Metz Attorney-Thomas H. Whaley et al.

[57] ABSTRACT I Synthetic lubricating oil composition comprising a major portion of an aliphatic ester base oil having lubricating properties formed by the reaction of a pentaerythritol or trimethylolpropaneand an organic monocarboxylic acid containing from about 0.01 to 2.5 weight percent of an imminium salt of thiocyanic acid represented by the formula:

,RRC=N HR SCN in which R represents anaromatic radical, a hydroxy aromatic radical or a conjugated olefinic radical having from 6 to 18 carbon atoms, R represents hydrogen or an aliphatic radical having from 1 to 12 carbon atoms and R" is an aliphatic radical having 1 to 20 carbon atoms, and from about 0.04 to 2 weight per cent of a polyhydroxy-substituted anthraquinone represented by the formula:

EF P- I 9 Claims, No Drawings SYNTHETIC AIRCRAFT TURBINE OIL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is concerned with a lubricating oil composition for a gas turbine or jet engine. Gas turbine aircraft engines are operated under extreme environmental conditions. External atmospheric temperatures are generally in the sub-zero range and internal engine temperatures are in the order of 400 500 F or above. These operating condition put severe stresses on the lubricating oil, so much so that the most advanced mineral lubricating oil compositions cannot be employed in gas turbine engines.

Synthetic ester base lubricating oil compositions containing a critically balanced blend of additives are being employed for lubricating gas turbine engines. These ester base oils are operative over a wide temperature range and exhibit good thermal stability, antiwear, load-carrying and anti-oxidation properties.

With the advent of advanced, more powerful gas turbine engines, higher levels of thermal and oxidative stresses are imposed on the lubricating oil composition. The present invention is directed to an improved synth etig este base lubricating oil composition.

2. Description of the prior art US. Pat. No. 3,330,763 discloses a synthetic lubricating oil composition having improved load-carrying properties employing a pentaerythritol ester base oil containing in combination an ammonium thiocyanate and a cyclic amine compound of the type represented by phenyl-alpha-naphthylamine.

A copending application Ser. No. 160,192 filed July 6, 1971 discloses a synthetic aircraft turbine lubricating oil composition containing an ammonium thiocyanate and a polyhydroxyanthraquinone.

SUMMARY OF THE INVENTION The synthetic lubricating oil composition of the invention comprises a major portion of an aliphatic ester base oil having lubricating properties containing in combination an imminium salt of thiocyanic acid represented by the formula:

in which R represents an aromatic radical, a hydroxy aromatic radical or a conjugated olefinic radical having from 6 to 18 carbon atoms, R represents hydrogen or an aliphatic radical having from 1 to 12 carbon atoms and R" is an aliphatic radical having 1 to 20 carbon atoms, and a polyhydroxy-substituted anthraquinone represented by the formula:

1. f Y A in which X, Y and Z each represent hydrogen or a hydroxyl group and at least one of these is a hydroxy] group.

More specifically, thee lubricating oil composition of the invention will consist of an ester base formed by the reaction of a pentaerythritol or trimethylolpropane and an organic monocarboxylic acid, from about 0.01 to 1.5 weight percent of the prescribed imminium salt of thiocyanic acid and from about 0.025 to 1 weight percent of the prescribed polyhydroxy-substituted anthraquinone.

This invention is based on the discovery that an ester base lubricating oil composition containing this specific additive combination has excellent load-carrying and corrosion inhibiting properties. This discovery was surprising since the prescribed imminium salts have little or no load-carrying properties when not employed in the specific combination of the invention. The structure of the prescribed hydroxy anthraquinone for an effective additive combination is also critical.

The base fluid component of the lubricant of the invention is an ester-base fluid prepared from a pentaerythritol or trimethylolpropane and a mixture of hydrocarbyl monocarboxylic acids. It is understood that di pentaerylthritol, tripentaerythritol and tetrapentaerythritol are suitable components of the ester base oil.

The hydrocarbon monocarboxylic acids which are used to form the ester-base fluid include the straight chain and branched chain aliphatic acids, cycloaliphatic acids and aromatic acids as well as mixtures of these acids. The acids employed have from about 2 to 18 carbon atoms per molecule, the preferred members having from 5 to 10 carbon atoms. Examples of suitable acids are acetic, propionic, butyric, valeric, isovaleric, caproic, decanoic, cyclohexanoic, naphtenic, benzoic acid, phenylacetic, tertiary-butylacetic acid and 2- ethylhexanoic acid.

In general, the acids are reacted in proportions leading to a completely esteritied pentaerythritol or trimethylolpropane with the preferred ester bases being the pentaerythritol tetraesters. Examples of commercially available tetraesters include pentaerythritol tetracaproate, which is prepared from purified pentaerythritol and crude caproic acid containing other C -C monobasic acids. Another suitable tetraester is prepared from a technical grade pentaerythritol and a rnbtture of acids comprising 38 percent valeric, 13 percent 2-methylpentanoic, 32 percent n-octanoic and 17 percent pelargonic acid. Another effective ester is the triester of trimethylolpropane in which the tirmethylolpropane is esterified with a monobasic acid mixture consisting of 2 percent valeric, 9 percent caproic, 13 percent heptanoic, 7 percent octanoic, 3 percent caprylic, 65 percent pelargonic and 1 percent capric acids. Trimethylolpropane triheptanoate, trimethylolpropane pentanoate and trimethylolpropane hexanoate are also suitable ester bases.

The ester base comprises the major portion of the fully formulated synthetic ester base lubricating oil composition. The ester base normally constitute at least percent of the lubricating oil composition and generally will comprise from about 90 to 98 percent of the lubricant.

The imminium salt of thiocyanic acid component of the lubricating oil composition of the invention is represented by the formula:

in which R represents an aromatic radical, a hydroxyaromatic radical or a conjugated olefinic radical having from 6 to 18 carbon atoms, R represents hydrogen or an aliphatic radical having from 1 to 12 carbon atoms and R" is an aliphatic radical having 1 to 20 carbon atoms.

Effective imminium salts of the thiocyanic acid conforming to the prescribed formula are prepared from the reaction of a suitable aldhyde with a suitable ammonium thiocyanate. Suitable aldehydes include benzaldehyde, salicylaldehyde, naphthaldehyde, tolualdehyde, anisaldehyde, cinnamaldehyde and crotonaldehyde. Suitable ammonium thiocyanates include mono-tertiary-C to C alkyl ammonium thiocyanate, mono-tertiary-C to C alkyl ammonium thiocyanate, dodecylammonium thiocyanate, 2-ethylhexylammonium thiocyanate, tertiary-octyl ammonium thiocyanate, tertiarybutyl ammonium thiocyanate and octadecyl ammonium thiocyanate.

Essentially equimolar amounts of a prescribed aldehyde and a prescribed ammonium thiocyanate are reacted to form an imminium salt of thiocyanic acid suitable for the lubricating oil composition of the invention.

The imminium salt of thiocyanic acid is employed in the lubricating oil composition of the invention in a concentration ranging from about 0.01 to 1.5 weight percent by weight of the lubricating oil composition. The imminium salt is preferably employed in a concentration ranging from about 0.05 to 0.25 weight percent.

The preparation of specific imminium salts of thiocyanic acid are set forth in the following examples.

EXAMPLE I 12.2 parts of salicylaldehyde, 37 parts of monotertiary-C to C alkylammonium thiocyanate, 1 part sodium chloride and 175 ml of toluene were reacted under reflux until the evolution of water ceased. The reaction mixture was concentrated in a rotary, dissolved in chloroform and filtered. 49 grams of product were recovered on removal of the chloroform. This product was the imminium salt represented by the formula H (Lima @011 in which R" represents a ten-C to C alkyl radical, analyzing 5.8 percent N, (theory 5.7 percent).

EXAMPLE II 12.2 parts of salicylaldehyde, 25.0 parts mono-terL-C to C -alkylammonium thiocyanate, 1 part sodium chloride and 175 ml of toluene were reacted as in Example I to form the imminium salt represented by the formula:

H c=r mwscn in which R" represents a terL-C to C alkyl radical, analyzing 8.0 percent N, (theory 7.9).

EXAMPLE I 21.2 parts of benzaldehyde, 50 parts mono-terL-C to C -alkylammonium thiocyanate, 1 part sodium chloride and 300 ml of toluene were reacted under reflux as in Example I to form 66 grams of the imminium salt represented by the formula:

in which R" represents a tern-C to C -alkyl radical analyzing Neutralization No. 166 (theory 166).

The second essential component of the lubricating oil composition is a polyhydroxy-substituted anthraquinone inhibitor represented by the formula:

(IDOH s/ 1 I 2 .llll. 5 4 YllX in which X, Y and Z each represent hydrogen or a hydroxyl group and at least one of these is a hydroxyl group. There is criticality in the structure of the polyhydroxy-substituted anthraquinone. This compound must have at least two hydroxyl groups and both of these must be attached to the ring carbon atoms in the alpha position to the quinone ring, i.e., on positions 1, 4, 5 and 8. Additional hydroxyl groups may be present without changing the effectiveness of the noted compounds. Compounds having only one hydroxyl group or compounds having more than one hydroxyl group but with only one on the l, 4, 5 and 8 carbon positions are not effective in the present invention. The specific polyhydroxy-substituted anthraquinones noted above must be employed with the prescribed imminium salt of thiocyanic acid to provide the improved lubricating oil composition of the invention.

Examples of effective polyhydroxy-substituted anthraquinones include l,4-dihydroxyanthraquinone, quinizarin, 1,5-dihydroxyanthraquinone, 1,2,4-trihydroxyanthraquinone, purpurin and l,2,5,8-tetrahydroxyanthraquinone.

The ineffective hydroxy-substituted anthraquinones include l-hydroxyanthraquinone, alizarin and 2,6-dihydroxyanthraquinone.

There is criticality in the concentration of the effective polyhydroxy-substituted anthraquinone inhibitor which must be employed in a concentration of at least 0.05 weight percent, the broad effective range being from 0.05 to 1 weight percent of the lubricating oil composition. The preferred concentration of this component is about 0.075 to 0.2 weight percent.

A fully formulated synthetic ester base lubricating oil composition for turbine engines will generally contain a number of additional additive components to enhance the performance and service life of the lubricating oil composition. A highly beneficial component for enhancing the oxidation resistance of the lubricating oil composition is an alkyl or alkaryl phenyl naphthylamine represented by the formula:

in which R is an alkyl or alkaryl having from about 4 to 12 carbon atoms. This radical canjbe a straight or branched chain alkylradicalwith the tertiary-alkyl structure being preferred or it can be an alkylaryl radical. The naphthylamine can be either an alpha or beta naphthylamine. Specific effective compounds of this class include N (p-t-octylphenyl)-alhpanaphthylamine, N-.(p-cumylphenyl)-6-cumylbetanaphthyl-amine, N-(p-t-octylphenyl)-betanaphthylamine: and the corresponding N-(p-tdodecylphenyl)-, N-(p-t-butylphenyly and N-(pdodecylphenyD-alpha and -beta-naphthylamines: These compounds, are fully described in U.S;' Pat. No. 3,414,618. They can be employed at a concentration from about 0.3 to 5 percent withthe preferred concentration being from about 0.5 to 2.5 percent.

The oxidation and corrosion resistance of the lubricating oil composition is increased by the employment of a dialkyldiphenylamine. These compounds are Compound bases were prepared using the foregoing Exter Base'from which lubricating oil compositions of the invention and similar comparison lubricants were prepared. The concentration of the additive components are in weight percent based on the total weight of the lubricant employed. Compounded Base A consisted of the foregoing Ester Base with 1.0 percent p,p'-di-tert.-octyldiphenylamine 2.0 percent tricresyl phosphate 1.5 percent N-(4-tert.-octylphenyl)-l-naphthylamine Compounded Base B consisted of ,the Ester Base, 1.0 percent p,p'-ditert.-octyldiphenylamine, 2.0 percent tricresylphosphate and 1.5 percent N-(4-cumylphenyl)-6-cumyl-beta-naphthylamine.

The lubricating oil composition of the invention and comparison fluids were tested to the Ryder Gear Scuff test designated Federal Test Method Standards 791, test method 6508. The results of this test are given in Table I below.

TABLE 1 Lubricating oil composition I Imminium salt H ydroxy anthraquinone Ryder gear Run Base 011 (wt. percent) (wt. percent) test p.p.i.

1 Compounded Base A 2, 215 2 Compounded Base B 2, 425 3 d 0. 1 s 2, 910 4 Quinizarm. 0. 1 2, 740 5 0.13 d .035 ,505 6 0.1 d 0.1 3,640 0.13 do 0. 06 3, 420

0. 1 Alizarin 0. 1 2, 695

represented by the formula: V

H R N in which R represents a hydrocarbyl radical such as an alkyl, aryl, alkaryl, cycloalkyl or aralkyl radical or mixture thereof having from 2 to 12 carbon atoms and preferably from 4 to 8 carbon atoms. Effective specific compounds include tricresylphosphate, cresyl diphenylphosphate, triphenylphosphate, tributylphosphate, tri(2-ethylhexyl)-phosphate and tricyclohexyl phosphate. This component can be employed at a concentration ranging from about 0.25 to 10 percent with the preferred concentration being from about 0.5 to 5 percent.

The Ester Base fluid had the following properties:

Viscosity, cs at 210 F 5.03 Viscosity, cs at 100 F 26.0 Viscosity, cs at F 6956 Viscosity Index 134.5 Flash, F 505 idis 6 tol0 in Table I illustrate the lubricating oil bricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and organic monocarboxylic acid having from about 2 to 18 carbon atoms per molecule containing:

a. from about 0.01 to 1.5 weight percent of an imminium salt of the thiocyanic acid represented by the formula: RR'C= NHR"-SCN in which R represents an aromatic hydrocarbon radical, a hydroxy aromatic hydrocarbon radical or a conjugated olefinic hydrocarbon radical having from 6 to 18 carbon atoms, R represents hydrogen or an aliphatic hydrocarbon radical having from 1 to 12 carbon atoms and R" is an aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, and

b. from about 0.05 to 1 weight percent of a polyhydroxy substituted anthraquinone inhibitor represented by the formula:

in which X, Y and 2 each represent hydrogen or a hy droxyl group and at least one of these is a hydroxyl group.

2. A lubricating oil composition according to claim 1 in which said imminium salt is represented by the formula:

in which R" represents a tertiary C to C aliphatic hydrocarbon radical.

3. A lubricating oil composition according to claim 1 in which said imminium salt is represented by the formula:

in-which R represents a tertiary C to C aliphatic hydrocarbon radical.

4. A lubricating oil composition according to claim 1 in which R" represents a tertiary C to C aliphatic hydrocarbon radical.

5. A lubricating oil composition according to claim 1 in which said inhibitor is purpurin.

6. A lubricating oil composition according to claim 1 in which said inhibitor is quinizarin.

7. A lubricating oil composition according to claim 1 in which said inhibitor is 1,5-dihydroxyanthraquinone.

8. A lubricating oil composition according to claim 1 in which said inhibitor is l,2,5,8-tetrahydroxyanthraquinone.

9. A lubricating oil composition according to claim 1 containing from about 0.05 to 0.25 weight percent of said imminium salt and from about 0.075 to 0.2 weight percent of said polyhydroxysubstituted anthraquinone. 

2. A lubricating oil composition according to claim 1 in which said imminium salt is represented by the formula:
 3. A lubricating oil composition according to claim 1 in which said imminium salt is represented by the formula:
 4. A lubricating oil composition according to claim 1 in which R'''' represents a tertiary C11 to C14 aliphatic hydrocarbon radical.
 5. A lubricating oil composition according to claim 1 in which said inhibitor is purpurin.
 6. A lubricating oil composition according to claim 1 in which said inhibitor is quinizarin.
 7. A lubricating oil composition according to claim 1 in which said inhibitor is 1,5-dihydroxyanthraquinone.
 8. A lubricating oil composition according to claim 1 in which said inhibitor is 1,2,5,8-tetrahydroxyanthraquinone.
 9. A lubricating oil composition according to claim 1 containing from about 0.05 to 0.25 weight percent of said imminium salt and from about 0.075 to 0.2 weight percent of said polyhydroxysubstituted anthraquinone. 